Edge seal for a semiconductor device and method therefor

ABSTRACT

In one embodiment, an edge seal region of a semiconductor die is formed by forming a first dielectric layer on a surface of a semiconductor substrate near an edge of the semiconductor die and extending across into a scribe grid region of the semiconductor substrate. Another dielectric layer is formed overlying the first dielectric layer. An opening is formed through the first and second dielectric layers. The second dielectric layer is used as a mask for forming a doped region on the semiconductor substrate through the opening. A metal is formed that electrically contacts the doped region and an exterior edge of the first dielectric layer within the opening.

BACKGROUND OF THE INVENTION

The present invention relates, in general, to electronics, and moreparticularly, to methods of forming semiconductor devices and structure.

In the past, the semiconductor industry utilized various methods anddevice structures to form semiconductor devices including discretedevices and integrated circuits. Most semiconductor devices had an edgeseal around the outside of the semiconductor die on which the device wasformed. The edge seal had various functions including maintaining auniform potential around the die, collecting charged contaminates,providing an electrical barrier to electrical contaminants along theedge of the active region of the die, providing a moisture barrier, andreducing cracking near the edge of the die. The edge seal normallyincluded a metalization layer that was formed near an edge of thesemiconductor device. Typically, several processing steps were requiredto form such edge seals. The various processing steps required to formthe edge seal generally increased the cost of the semiconductor device.One example of such an edge seal was disclosed in U.S. Pat. No.6,078,068 that issued to Ronald Tamura on Jun. 20, 2000.

Accordingly, it is desirable to have an edge seal structure and a methodof forming an edge seal that uses fewer processing steps and that has alower cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an enlarged cross-sectional view of a edge sealaccording to the prior art;

FIG. 2 illustrates an enlarged plan view of an embodiment of a portionof a semiconductor wafer on which a plurality of semiconductor die areformed in accordance with the present invention;

FIG. 3 illustrates an enlarged cross-sectional view of a portion of anembodiment of the plurality of semiconductor die of FIG. 1 in accordancewith the present invention;

FIG. 4-FIG. 6 illustrate enlarged cross-sectional views at variousstages of forming the plurality of semiconductor die of FIG. 1 inaccordance with the present invention; and

FIG. 7 illustrates an enlarged cross-sectional view of an embodiment ofa portion of another plurality of semiconductor die that are analternate embodiment of the plurality of semiconductor die of FIG. 1 inaccordance with the present invention.

For simplicity and clarity of the illustration, elements in the figuresare not necessarily to scale, and the same reference numbers indifferent figures denote the same elements. Additionally, descriptionsand details of well-known steps and elements are omitted for simplicityof the description. For clarity of the drawings, doped regions of devicestructures are illustrated as having generally straight line edges andprecise angular corners. However, those skilled in the art understandthat due to the diffusion and activation of dopants the edges of dopedregions generally may not be straight lines and the corners may not beprecise angles.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a prior art edge seal region of a prior artsemiconductor die. A portion of a semiconductor die 500 is masked andthe exposed portion is oxidized to form a field oxide region 503. Theprocess of forming field oxide region 503 is usually referred to aslocal oxidation of silicon or LOCOS. Field oxide region 503 is used as amask for implanting a doped region 502 in substrate 501 that isself-aligned to one edge of region 503. Region 502 generally is formedalong with doped regions within an active area of die 500. The activearea is to the left of field oxide region 503. The dopant species ofdoped region 502 generally is also activated along with the other dopedregions of die 500. Subsequently, an oxide layer 504 is formed on fieldoxide region 503 and the adjacent exposed surface of substrate 501.Layer 504 usually extends to an edge 510 of die 500. A mask is appliedand patterned, and layer 504 is etched to form an opening overlyingdoped region 502. Thereafter, a metal is deposited into the opening toelectrically contact doped region 502. A metal mask is subsequentlyapplied and patterned, and portions of the metal are removed, such as byan etching step. Subsequently, inter-layer dielectric layers, such aslayer 506, and other metal layers, such as layers 505 and 507, may beformed as desired. As can be seen, several process steps are requiredfor masking and implanting region 502, masking and forming layer 504,masking and forming the opening in layer 504, and masking and formingmetal layer 505. All of these process steps add to the cost of die 500.

FIG. 2 illustrates an enlarged plan view of a portion of a semiconductorwafer 25 on which an embodiment of a plurality of semiconductor die,such as a die 26 and a die 27, are formed. Die 26 includes an interiorsection where passive devices and active devices, such as transistorsand diodes, are formed. A plurality of bonding pads 29 are outside ofthe interior section toward an outside edge of die 26. An exemplaryembodiment of an edge seal region or edge seal 30 is positioned betweenthe plurality of bonding pads 29 and the exterior edge or outside edgeof die 26. Similarly, die 27 includes an interior section where passivedevices and active devices are formed. A plurality of bonding pads 37are outside of the interior section toward an exterior edge or outsideedge of die 27. An exemplary embodiment of an edge seal region or edgeseal 38 is positioned between plurality of bonding pads 37 and theoutside edge of die 27. Dice 26 and 27 generally have scribe grids alongeach side of the semiconductor die as illustrated by scribe grids 32,33, and 34.

FIG. 3 illustrates an enlarged cross-sectional view of a portion of dice26 and 27 that includes scribe grid 33 and the exemplary embodiments ofedge seals 30 and 38. This description has references to FIG. 2 and FIG.3. As will be seen further hereinafter, edge seal 30 is formed toinclude a metal layer 46 that is positioned to electrically contact adoped region within a substrate of the die and that also contacts anexterior edge or outside edge of a thick dielectric layer, for example afield oxide layer, that is on a surface of a semiconductor substrate ofthe die.

In the preferred embodiment, die 26 and 27 are vertical power MOStransistors and are illustrated to have a single metal interconnectlayer. However, those skilled in the art will appreciate that edge seals30 and 38 may be formed on integrated circuit die that have variousnumbers of active transistors along with a plurality of metalinterconnect layers and associated inter-layer dielectrics. Dice 26 and27 are formed on a semiconductor substrate 57 that includes a bulksemiconductor substrate 55 and an epitaxial layer 56 that is formed onbulk semiconductor substrate 55. In some embodiments, epitaxial layer 56may be omitted or may be replaced by a doped region of substrate 57.

For the exemplary embodiment illustrated in FIG. 3, die 26 includes athick dielectric layer 43, such as a field oxide layer, an inter-layerdielectric 44 that is formed on layer 43, another dielectric layer 45(such as a passivation layer) on dielectric 44, and a metal layer 46that is positioned on substrate 57 and abutting layer 43. Similarly, die27 includes a thick dielectric layer 48, such as a field oxide layer, aninter-layer dielectric 49 that is formed on layer 48, another dielectriclayer 50 (such as a passivation layer) that is formed on dielectric 49,and a metal layer 52 that is positioned on substrate 57 and abuttinglayer 48. Scribe grid 33 includes a portion of wafer 25 that ispositioned between metal layers 46 and 52, and has a width or distance35 as illustrated by an arrow. Those skilled in the art will appreciatethat the width of scribe grid 33 extends between metal layers 46 and 52,but that only a portion of the width is removed when die 26 and 27 aresingulated from wafer 25. Those skilled in the art will also realizethat metal layers 46 and 52 may or may not be covered with furtherdielectric or metal layers. The region of wafer 25 where exterior edgesor outside edges 61 and 62 of respective dice 26 and 27 willsubsequently be formed are illustrated in general by dashed lines.

FIG. 4 illustrates an enlarged cross-sectional view of wafer 25 at anearly stage in the formation of die 26 and 27. Prior to forming activedevices within the interior section of die 26 and 27, a thick dielectriclayer 39 is generally formed on the surface of wafer 25. In mostembodiments, dielectric layer 39 is formed as a field oxide region bythermal oxidation of a portion of substrate 57. During this formationstep, layer 39 preferably is formed to extend across the entire width ofscribe grid 33 and generally extends to the active regions of dice 26and 27. Those skilled in the art will appreciate that layer 39 usuallyis masked from some of the active regions within the interior section ofdice 26 and 27. In alternate embodiments, dielectric layer 39 may beother types of thick dielectrics that are formed on the surfacesubstrate 57 and that are used to minimize breakdown between differentregions of die 26 or die 27. For such an alternate embodiment,dielectric layer 39 may be applied as a blanket layer that covers thesurface of wafer 25 and is then patterned within the interior section ofdice 26 and 27. However, the portion of layer 39 within scribe grid 33that extends to the interior section of dice 26 and 27 would not bepatterned during those steps. For example, dielectric layer 39 may be alayer of silicon dioxide or silicon nitride that is deposited on thesurface of wafer 57. In some such alternate embodiments, a thin layer ofsilicon dioxide may be formed on the surface of wafer 57 prior toforming dielectric layer 39 as illustrated by a dashed line 85.Typically, this is a surface layer of silicon dioxide that usually is atleast an order of magnitude thinner than the thickness of layer 39.Layer 39 generally has a thickness that is greater than approximately0.2 microns.

After forming layer 39, the doped regions of the active and otherportions of die 26 and 27 typically are formed within the interiorsections of dice 26 and 27. During those doping steps, layer 39 acts asa blocking layer to prevent doping the portion of wafer 25 that includesscribe grid 33 and the region where layers 46 and 52 are to be formed.Thereafter, a dielectric layer 40 is formed on layer 39 and on theinterior sections of die 26 and 27 to function as an inter-layerdielectric that facilitates forming single layer or multi-layermetalization on the interior sections of die 26 and 27. As is well knownto those skilled in the art, layer 40 generally is applied as a blanketlayer that covers all of layer 39 and then patterned to form openings asrequired to make appropriate electrical connections within the interiorsection of dice 26 and 27. After all the metal interconnections areformed and bonding pads are formed for dice 26 and 27, anotherdielectric layer 41 may be formed on dielectric layer 40 to function asa passivation layer that covers all of wafer 25. Those skilled in theart will appreciate that other dielectric layers and metal layers may beformed between layer 40 and layer 41 if more metal interconnect layersare used within the interior section of dice 26 and 27.

FIG. 5 illustrates a subsequent stage in the process of forming dice 26and 27. A mask, illustrated by dashed lines 76, is applied and patternedto expose portions of layer 41 (FIG. 4) that overlie the bond pad areasof the die and that also overlie the region where grid 33 and metallayers 46 and 52 are to be formed. The opening in the mask overlyingscribe grid 33 and metal layers 46 and 52 has a width 36. The maskusually covers substantially the remainder of dice 26 and 27 exceptwhere other scribe grids, such as scribe grids 32 and 34, and associatededge seal metal layers, are to be formed. The opening in the mask isused to simultaneously form an opening through layer 41 to the bond padsand through layers 41, 40, and 39 to expose the surface of substrate 57within the opening. After forming the opening, the portions of layer 41that remain overlying dice 26 and 27 are illustrated as dielectriclayers 45 and 50, respectively. The portions of dielectric layer 40 thatremain overlying die 26 and 27 are illustrated as dielectric 44 andlayer 49, respectively. Similarly, the portions of layer 39 that remainoverlying dice 26 and die 27 are illustrated as respective dielectriclayers 43 and 48. Exterior edges of layers 43-45 and 48-49 are exposedalong the sidewalls of the opening. Mask 75 is removed and the exposedportion of the surface of substrate 57 is doped to form a doped region42 on the surface of substrate 57 and within the opening. Typically, thedopants are implanted through the opening and layers 45 and 50 functionas a mask that prevents doping other portions of dice 26 and 27. Sincethe dopants within the interior section of dice 26 and 27 are alreadyactivated and metal is already applied in these interior sections, thedopants within region 42 usually do not receive an activation step. Thehigh temperatures of an activation step could damage the active areasand metal layers within the interior section of dice 26 and 27.Thereafter, a metal layer 59 is formed as a blanket layer that coversdielectric layers 45 and 50 in addition to the exposed surface ofsubstrate 57.

Referring back to FIG. 3, metal layer 59 is anisotropically etched toremove the portions of metal layer 59 that are on dielectric layers 45and 50 and on most of the surface of doped region 42 but leave portionsof layer 59 as metal layers 46 and 52 that electrically contact dopedregion 42. Because of the blanket deposition and anisotropic etching,metal layer 46 mechanically abuts the exterior edges or outside edges oflayer 43, dielectric 44, and layer 45 in addition to abutting andelectrically contacting doped region 42. Similarly, metal layer 52mechanically abuts the exterior edges of layers 40, 49, and 50 inaddition to abutting and electrically contacting doped region 42. Itshould be noted that in another embodiment it may also be possible touse a patterned photo resist layer to mask all of or portions of theanisotropic etching of metal layer 59. Subsequently, wafer 25 usually isheated to a temperature required to sinter metal layers 46 and 52. Wafer25 is heated to a temperature of approximately three hundred to sixhundred degrees Celsius (300-600° C.) and preferably to about fourhundred twenty five degrees Celsius (425° C.). Additionally, because ananisotropic etch is used, no masking step is required to form metallayer 59 into metal layers 46 and 52. Even though the dopants of region42 do not receive an activation step, the dopants usually are heatedduring the steps of forming metal layer 59 and the patterning requiredto form metal layers 46 and 52. An ohmic contact is formed betweenregion 42 and metal layers 46 and 58. In the preferred embodiment, bulksubstrate 51 and layer 56 are N-type material, region 42 is N-Typematerial having a peak doping concentration no less than about 1×10²⁰atoms/cm³, and the material used for metal layers 46 and 52 is aluminum.The resulting structure forms an ohmic contact between region 42 andlayers 46 and 52. In the preferred embodiment of a vertical power MOStransistor, substrate 57 usually forms a drain region of the transistor,thus, layers 46 and 52 generally are not electrically connected to anyother potential other than the electrical potential received throughsubstrate 57 and region 42. In other embodiments, such as an integratedcircuit, layers 46 and 52 may be electrically connected to a bonding padthat is expected to be connected to a common ground potential of theintegrated circuit.

Referring now to FIG. 6, wafer 25 is singulated to separate the dice onwafer 25 such as by scribing through scribe grids 32, 33, and 34 therebysingulating die 26 and 27. The process of singulating die 26 and 27removes a vertical portion of wafer 25 between dice 26 and 27 andexposes outside edges 61 and 62 of respective dice 26 and 27. Aftersingulation, metal layer 46 is a distance 60 from outside edge 61 of die26. Distance 60 is illustrated in general by an arrow. Similarly, metallayer 52 is a distance 63 from edge 62. Typically, distance 35 isbetween about seventy-five and one hundred (75-100) microns anddistances 60 and 63 are about twenty to thirty (20-30) microns. Formingthick dielectric layer 39 (including layers 43 and 48), dielectric layer40 (including dielectrics 44 and 49), and dielectric layer 41 (includinglayers 45 and 50) to extend into edge seals 30 and 38 and into thescribe grid, and subsequently forming an opening through them to formdoped region 42 and metal layers 46 and 52 minimizes the number ofprocessing operations required to form edge seals 30 and 38.

FIG. 7 illustrates an enlarged cross-sectional portion of an alternateembodiment of edge seals 30 and 38. For the embodiment illustrated inFIG. 7, dielectric layers 39 and 40 are formed as explained in thedescription of FIGS. 3-4. Thereafter, a metal layer 70 is formed onlayer 40 to function as an electrical contact to metal layers 46 and 52.Subsequently another inter-layer dielectric 71 may be formed on metallayer 70. Other metalization layers may also be used to form amulti-layer metal system. For example, another metal layer 72 may beformed on dielectric 71 and a passivation layer 73 may be formed onlayer 72 and exposed portions of dielectric 71. A mask (not shown) isapplied and patterned to form an opening having a width 36 to exposewhere scribe grid 33 and metal layers 46 and 52 are to be formed. Theexposed portions of layers 71-73 and 43-44 are removed to expose thesurface of substrate 57. The mask is removed and layer 73 functions as amask during the formation of doped region 42. Subsequently, a metal isblanket deposited and anisotropically etched to any depth to form metallayers 46 and 52 that not only electrically contact doped region 42 butalso electrically contact metal layer 70. Thereafter, wafer 25 issintered and dice 26 and 27 are singulated.

In view of all of the above, it is evident that a novel semiconductordevice and method is disclosed. Included, among other features, isforming a plurality of dielectric layers extending from an edge sealregion of a one die across a scribe grid to an edge seal region of anadjacent die. One etching operation is used to form an opening throughthe plurality of dielectric layers to expose a portion of the underlyingsubstrate between the two die. Subsequently, a top dielectric layer ofthe plurality of dielectric layers is used as a mask to form a dopedregion in the substrate through the opening followed by forming metallayers on the doped region and abutting outside edges of the dielectriclayers that are exposed within the opening. These process steps minimizethe number of masking and processing operations required to form thedevice there by reducing the cost thereof.

While the subject matter of the invention is described with specificpreferred embodiments, it is evident that many alternatives andvariations will be apparent to those skilled in the semiconductor arts.More specifically the subject matter of the invention has been describedfor a particular P-channel vertical power MOS transistor structure,although the method is directly applicable to other vertical power MOStransistors, as well as to other types of semiconductor die includingintegrated circuits having a plurality of transistor types.

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 18. A method of forming an edge sealregion of a semiconductor die comprising: forming a first dielectriclayer on a substrate adjacent to a scribe grid area of the substrate;forming a second dielectric layer overlying the first dielectric layer;forming a doped region on the substrate and self-aligned to an edge ofthe second dielectric layer; and forming a metal spacer on the dopedregion and self-aligned to an edge of the first dielectric layer. 19.The method of claim 18 wherein forming the doped region on the substrateincludes forming a passivation layer overlying the second dielectriclayer and using the passivation layer as a mask to form an openingthrough the second dielectric layer and the first dielectric layer andfurther including forming the doped region through the opening thenforming the metal spacer through the opening.
 20. The method of claim 18wherein forming the metal spacer includes forming the metal spacer andleaving a surface of the substrate that is abutting the metal spacer anddistal from the first dielectric layer exposed, and further includingcutting through the substrate where the surface of the substrate isexposed.
 21. The method of claim 18 further including forming activeregions of the semiconductor die in an interior section of thesemiconductor die before the step of forming the doped region on thesubstrate wherein forming the active regions include forming activedoped regions and activating dopants within the active doped regions;wherein the step of forming the doped region includes not performing anactivation step after forming the doped region on the substrate; andwherein the step of forming the metal spacer includes not exposing thesemiconductor die to a temperature that is greater than a temperaturerequired to sinter the metal spacer.
 22. The method of claim 18 whereinforming the metal spacer includes forming a metal layer overlying thesecond dielectric layer and on the substrate overlying the doped region;and anisotropically etching the metal layer to remove first portions ofthe metal layer and leave second portions of the metal abutting the edgeof the first dielectric layer as the spacers.
 23. The method of claim 18wherein forming the doped region on the substrate includes forming anopening through the first and second dielectric layers and exposing thesubstrate, and forming the doped region through the opening subsequentto the step of forming the second dielectric layer.